What happens when the cut off valves don't function properly?

the cut off valves effect idle circuit only you can get just the jet to replace the cut off valve, better option, if the carbs are tuned properly the engine will not run on, (which is the only reason for the cut off valves being there), it will always be worse at warm up but with faulty cut off valves idle will always be a problem it will probably be worse on the left carby than the right, since the left carby actually controls the idle system.